Tubular structures (or “tubes”) can be used to convey a fluid through a heat exchanger while transferring thermal energy (heat) to or from another fluid passing over the outer surfaces of the tubes, thereby effecting a transfer of heat while maintaining a physical separation of the two fluids. By way of example, such structures find particular utility in industrial steam generation or process fluid heat exchange, automotive heat exchange components, and space heating and cooling, among other heat transfer applications. The geometry of the tubes themselves varies from application to application, and includes cylindrical, oval, rectangular, as well as other shapes that may be desirable for a given usage.
In many cases it is desirable to increase the rate of heat transfer between the fluid flowing through the tubes and the inner wall surfaces of the tubes, thereby reducing the overall required size of the heat transfer equipment. Such increase can be accomplished by incorporating features to turbulate the fluid as it flows through the tubes, thus eliminating or reducing the formation of a fluid boundary layer on the inner wall surfaces. It is known that a fluid boundary layer inhibits the efficient transfer of heat between the bulk fluid and the wall, due to the need for transfer of the heat energy via conduction through the relatively slow-moving layers of fluid adjacent the walls.
Although many methods of turbulating the flow are known in the art, one method commonly used in certain applications (automotive radiators, by way of an example) includes providing multiple protrusions extending from the tube wall into the fluid volume. These protrusions disrupt the formation of a fluid boundary layer and promote turbulence in the fluid flow in order to improve the rate of heat transfer. Protrusions of this kind are often referred to as “dimples”, and such tubes are referred to as “dimpled” tubes.
As a generally undesirable side effect, the turbulence produced by such protrusions also tends to result in an increase in the pumping power required to move the fluid through the tubes. This necessitates a trade-off between the advantages of increased heat transfer performance on the one hand, and the disadvantages of increased pressure drop on the other. Attempts by heat exchanger designers to optimize this trade-off have resulted in the continuous development of new dimple geometries and patterns.